1. Field of the Invention
This invention relates generally to data communications and more particularly to data communications using multiple networks.
2. Description of the Prior Art
With the increase usage of digital computers, data communication between these digital computers has become very important. Commonly, this data communication is between a user terminal and a computer but in more sophisticated systems will occur between several terminals and several computers. In addition, peripherals such as printers and mass memory devices may be included. This data communications configuration is referred to as a network. Often times, data is transmitted through a communications network or channel by a transceiver sometimes referred to as a MODEM.
Several different types of physical layers or transmission media have been used previously to provide data communications between computer devices. One type, disclosed in U.S. Pat. No. 4,365,331 includes a single coax cable that is connected to several MODEMs where each MODEM provides a network interface to at least one device. Data is communicated over the coax cable by multiple frequency carrier transmissions taking advantage of the coax cable's broad bandwith capacitlity. Another type of physical layer includes several pairs of twisted wire.
It is an object of the present invention to provide a data communication network interface that permits communications between two electrically different physical layers in a manner that provides for simultaneous transmission of data information or information traffic on both physical layers. This capability allows terminals each connected to different physical layers to communicate as if the terminals were on the same physical layer.
When a multiple of devices are connected to a single communciations network, communications is established between devices by one device accessing the network when the network is inactive and calling the address of the device it wishes to communicate with. Often problems occur when two terminals attempt to access the network at the same time resulting in a data collision.
It is another object of the present invention to provide a system which will prevent a device from accessing the network when the network contains information traffic thus preventing or at least minimizing data collisions.